1. Field of the Invention
The present invention relates to a system and method for treating farm animal waste, such as hog and poultry waste, to remove volatile organic compounds (VOCs) from wastewater treatment pits and thus control smell. The farm animals are housed in structures equipped with grated flooring to permit animal waste to fall into pits below. The pits contain water inoculated with a special assemblage of natural microbes to which oxygen is supplied through PVC piping arranged in the pits. These special microbes have an affinity for ammonia and convert much of the animal waste into carbon dioxide, fatty acids, and water.
The system of the invention also includes a second piping network situated between the wastewater treatment pits and the grated flooring which serves to create a negative air situation by which escaping foul-smelling air is pulled back into the wastewater to permit further action on the VOCs by the microbes in the water.
This bioremediation process results in less odor emitted and fewer waste solids to be disposed of, further processed, or placed directly in storage lagoons.
2. Description of the Prior Art
There has been an ongoing conflict between environmentalists and large-scale livestock producers, particularly hog and chicken farmers. In the case of hog farming, lagoons are used as outdoor storage for animal waste. These lagoons can vary in size from less than an acre to more than 25 acres. Typically, hogs are housed in structures with slatted decks or otherwise grated floors so as to allow excrement to fall through the openings in the grating into wastewater pits below the grating. The animal excrement is stored in the pits until being emptied into one of the aforesaid holding lagoons.
Animal waste pits currently in operation vary in depth as well as in frequency of solid waste removal. Hog waste systems in the Eastern and Southeastern United States utilize pits with water about 12 inches deep. About every 7 days, the pits are emptied into a holding lagoon. Water from the top of the lagoon is pumped back to recharge the pits after waste solids have settled in the lagoon. When soil conditions permit, water from the lagoon is sprayed on crop land for fertilization to prevent the lagoon from overflowing. In colder regions, the pits may be much deeper to permit storage for longer periods or until application to crop land by spraying is possible.
These lagoons leak manure into underground water systems, and carry a very offensive odor. The odor from such farms has caused environmentalists and individual land owners to call for a ban on open-air manure lagoons, or at least very strict government regulation of same, including limitations on when hog effluent may be sprayed as fertilizer on surrounding fields. The stench intensifies with larger quantities of waste, higher ambient air temperature, and poor air quality in general, among other factors.
There has also been an established link between hog farm odors and illness in people inhabiting the areas adjacent large hog facilities. Researchers at the University of Iowa found an unusually high rate of respiratory problems among people who lived near a 4,000-sow hog confinement facility. The symptoms, which include chronic bronchitis, occupational asthma, chronic sinusitis, and organic dust syndrome, were similar to those documented among hog factory workers worldwide, and are believed to be attributable, at least in part, to the toxic gases hydrogen sulfide and ammonia associated with hog waste odor.
There therefore exists a need for efficient methods and systems to reduce the amount and/or intensity of odors emanating from hog farm waste lagoons which is both economical and adaptable to various sizes of farming establishments.
In conventional treatment systems, the animal waste is left to be broken down in the lagoons by natural anaerobic microorganisms, which results in very foul odors. It would be prohibitively expensive to equip these large lagoons with motors and supply the power for oxygen to support aerobic microorganisms which would give off less disagreeable odors and break down the waste solids faster. In addition, the prior art systems depend on indigenous microbes that vary in effectiveness geographically.
Many technologies are now being tested to control animal waste odors and to affect the nitrogen and phosphorus content of the waste solids. These methods include additives to the diet, separation of solids, chemical processing of the waste solids, composting, catalytic reactors, etc.
For example, researchers at Purdue University have investigated the relationship between manure odor and swine diets, and have found that reducing the crude protein in the hogs' diet and supplementing it with essential amino acids effectively reduces nitrogen excretion by 20-42% and ammonia concentration by 25-42% . However, smaller hog farmers may not be able to afford or may be unwilling to invest in odor-control technologies that do not add to farm profitability.
A cultured wetlands approach has been used successfully worldwide to reduce odors using a bacteria spread over the surface of the wetlands to digest the nutrients, antibiotics and heavy metals contained in the manure. However, a typical cultured wetlands approach involves the creation of about one mile of push-up terraces and six water channels over a 5-acre plot. Gates between the water channels must also be erected to allow for water flow. Moreover, the bacteria requires a 10 day incubation period before it is effective in degrading the manure. Obviously, this approach is too time, cost, and land consuming to be feasible in many animal farm establishments.
The "Slurry/Masster" technology which is known in the art separates the solids from the liquids in hog manure by adding a chemical to the slurry that causes clumping or flocculation. Once the slurry has been mixed with the flocculants, it is passed over a screen to separate the solids from the liquids, where the liquids are directed to irrigation pipes and the solids are processed into fertilizer.
Researchers at Southern Illinois University are developing a catalytic reactor that could cut swine barn odors caused by para-cresol, a highly concentrated chemical compound found in swine buildings. The building's air is drawn through catalytic converters to speed up the reaction between para-cresol and oxygen to produce carbon dioxide and water. This system will require both high temperature (about 150.degree. C.) and a synthesized catalyst capable of breaking down para-cresol completely.
Some hog farms in the far North and Northwestern United States have utilized chopped straw to cover clay-lined manure storage basins in an attempt to reduce odor. Straw covers have been used in Canada in this manner for 10-15 years. However, manure lagoons are not used in hog farming in these geographical errors.
U.S. Pat. No. 5,176,823 shows an odor control system incorporating a conventional hood apparatus over a wastewater settling tank to draw air containing VOCs from the waste into a scrubber.
U.S. Pat. No. 5,472,472 describes a process for converting animal waste excrement into ecologically manageable materials. The solids in an aqueous slurry of animal excrement are precipitated in a solids ecoreactor. The treated slurry is then passed to a bioreactor zone where soluble phosphorus is precipitated with metallic salts. The remaining slurry is then aerobically and anaerobically treated to form an active biomass that actively bioconverts the remaining soluble phosphorus, and the slurry is passed to an ecoreactor zone for conversion to a beneficial humus material. Reduction of odor is a side effect of this process. However, the apparatus and procedure is cumbersome and costly, and would not be feasible for hog farmers who do not also trade in soil enhancing products.
Thus, there remains a need in the industry for a system that will effectively bioremediate a wide range of gases and volatile organic compounds in order to reduce animal waste effluvia as well as the amount of solid material in animal waste pits. The system should also be useable in varying geographical regions and in animal farming establishments of varying size and sophistication.